Case history and back-analysis of large-scale embankment construction on peat using vacuum consolidation

¹ DOCON Co., Ltd., Sapporo, Japan
² Kinjo Rubber Co., Ltd., Osaka, Japan
³ Graduate School of Engineering, Hokkaido University, Sapporo, Japan
⁴ Faculty of Engineering, Hokkaido University, Sapporo, Japan

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

This presentation discusses engineering considerations for designing and constructing large-scale embankments on peat deposits in Hokkaido, northern Japan, using the vacuum consolidation method with Prefabricated Vertical Drains (PVDs). Field measurements revealed that the pore water pressure behavior of peat between drains differs markedly from that of clay. To investigate the mechanism underlying this difference, axisymmetric elasto-plastic finite element analyses were performed on a unit cell containing a PVD. The permeability and consolidation coefficient of the peat decrease significantly during compression, resulting in the delayed dissipation of excess pore water pressure. Under vacuum consolidation, negative pressure is rapidly applied around the drains, accelerating consolidation and further reducing permeability near the drains. This leads to slower dissipation of excess pore water pressure at midpoints between drains, a trend successfully reproduced in analyses that considered a variable coefficient of consolidation. Consequently, peat exhibits a larger discrepancy between settlement-based and effective stress-based degrees of consolidation than clay. This difference has significant implications for estimating strength gain during vacuum consolidation. Exploiting the effective stress‑based degree of consolidation provides a rational and reliable approach for predicting strength gain for design in peat deposits subjected to vacuum consolidation.